This study of song perception by songbirds will contribute to the long-term goal of understanding neural mechanisms underlying human perception of speech. The focus of these experiments is the role of auditory neurons (HVc nucleus) in categorical perception (CP), wherein continuous differences in song stimuli are perceived as instances of discrete categories. Previous behavioral tests have revealed features of birdsong that evoke CP in swamp sparrows, and those features will be duplicated in this study. In the first experiment, intracellular recordings of HVc neurons will reveal whether individual neurons express categorical responses to song stimuli. If categorical responses are evident, comparison of subthreshold and action potential responses will reveal whether categorical boundaries are established in HVc or in sites presynaptic to HVc. In a second experiment, extracellular recordings of HVc neurons in awake and freely behaving birds will reveal whether categorical behavioral responses to song stimuli are accompanied by categorical responses of HVc neurons. These data will provide new insight into the role of HVc neurons in the perception of auditory signals and may suggest mechanistic features of human perception of speech. [unreadable] [unreadable]